This invention relates generally to sensors and more particularly to linear displacement sensors for use in aerospace control systems and the like for converting mechanical displacement inputs into electrical outputs.
It is known to detect discrete actuator and/or actuator linkage positions in aerospace systems and the like using electromechanical limit switches or electronic proximity switches. These devices provide a change in an electrical output signal when the actuator reaches a selected position to trip the respective switch. It is also know to detect actuator position along a full range of travel using linear variable displacement transducers (LVDTs) based on the inductive relationship between a core movably mounted within a coil providing an electrical output proportional to the position of the core.
Electromechanical switches have a relatively low cycle life due to the inherent nature of mechanical switching parameters which change over time, including contacts to wear, blades to fatigue and the like. LVDTs and electronic proximity switches on the other hand, typically require expensive secondary electronics to interface with aerospace platforms and proximity switches have a further limitation in that they require the use of targets or special actuator material.
It is an object of the invention to provide a relatively low cost linear displacement sensor having long cycle life particularly useful in aerospace applications. Another object of the invention is the provision of an aerospace grade linear displacement sensor which overcomes the limitations in the prior art noted above.
Briefly described, an aerospace grade linear displacement sensor made in accordance with the invention includes a pushbutton movably mounted on a housing for applying a force through a spring to a movable capacitor plate disposed on a diaphragm of a variable parallel plate capacitive transducer disposed in the housing. The pushbutton comprises an elongated tubular member slidably received in a mounting sleeve portion forming a part of the housing. A coil spring is disposed inside the tubular pushbutton member with one end of the spring seated in a closed force receiving end of the tubular pushbutton member and the other end of the spring seated on the head of a plunger which extends to the diaphragm surface of the variable parallel plate capacitive transducer along an axis which is coaxial with the longitudinal axis of the transducer. The diaphragm of the variable parallel plate capacitive transducer is sealingly attached to a first face surface of a substrate with electrical terminals extending through the substrate to an opposite second face surface. An electronics chamber is formed in the housing on the second face surface side with signal conditioning electronics disposed in the chamber connected to the terminals and to output leads which extend outside the housing.